Arrangements relating to the printing ribbon in printing machines



Nov. 28, 1967 Y. c. DOLLOT 3,354,822

ARRANGEMENTS RELATING TO THE PRINTING RIBBON IN PRINTING MACHINES Flled Jan 17 1966 6 Sheets5heet 1 Nov. 28, 1967 Y. c. DOLLOT ARRANGEMENTS RELATING TO THE PRINTING RIBBON IN PRINTING MACHINES Filed Jan. 17, 1966 6 Sheets-Sheet 2 Nov. 28, 1967 Filed Jan. 17, 1966 Y. c. DOLLOT 3,354,822

ARRANGEMENTS RELATING TO THE PRINTING RIBBON IN PRINTING MACHINES 6 Sheets-Sheet 3 Nov. 28. 1967 Y. c. DOLLOT 3,354,822

ARRANGEMENTS RELATING TO THE PRINTING RIBBON IN PRINTING MACHINES Filed Jan. 17, 1966 6 Sheets-Sheet 4 Len cls ca 050 +46v ---46v 1, J05 JO2 H05 N05 OO5 MO6 N06 1 {cues cwos v-- i b: b: 5' 0005 W06 5 4 WMMWJ'W .BY Am; mum! vv- 28. 1967 Y. c. DOLLOT ARRANGEMENTS RELATING TO THE PRINTING RIBBON IN PRINTING MACHINES Flled Jan 17 1966 6 Sheets-Sheet 6 CH0? CHOG United States Patent 5 Claims. 331. 101-336) The present invention relates to improvements in sys tems for moving the printing ribbon in printing machines.

These feed systems are designed to move the inked ribbon employed in the printing alternately in one of two opposite directions, the reversal of the direction of movement of the ribbon taking place when the latter has reached either one of its two ends. The inked ribbon thus performs a series of forward and backward travels, whereby it is possible to obtain a large number of high-quality impressions with the same ribbon. This mode of utilisation is found to be the more advantageous with a moist ribbon since, after each passage, the ink remaining in the ribbon is redistributed therein by capillary action.

In methods for printing characters which are visually identifiable and can be automatically scanned by optical, magnetic or other methods, it is essential for the printing to be of very high quality in order that the scanning of these characters may thereafter take place by means of appropriate detecting members with a minimum danger of errors. By reason of this condition, there is used for the printing a dry ribbon in which all the ink actually utilised for the printing of the characters is completely transmitted from the ribbon to the paper to be printed on, because the ink necessary for the formation of each character must be transferred in a well-defined quantity in order that it may have appropriate, for example optical or magnetic, properties which can act effectively and correctly on the corresponding detecting members. Consequently, that portion of the said total-transfer dry ribbon which has already served for the printing cannot be reused, and the said ribbon is therefore fed only in one direction. In addition, when a line of characters has been completely printed on the paper, it is essential to move this ribbon to a sufficient distance to prevent the inked portion which is then positioned opposite the striker hammers from interfering with that portion which has previously been used. This condition requires that the dry total-transfer ribbon be moved very rapidly at each line shift through a distance at least equal to the height of a printed character,- the movement of the ribbon being stopped at the time when a line is printed. This mode of feed makes it possible to effect a considerable saving of ribbon, which is the more appreciable since the latter can be used only once.

An object of the present invention is to improve the systems employed for feeding an ordinary wet or dry partial-transfer ribbon to enable them also to be employed in devices for feeding a total-transfer dry ribbon.

In accordance with the present invention there is provided a system for moving an inked ribbon in a printing mechanism in either of two opposite directions or, where necessary, in only one direction, one of the two ends of the ribbon being fast with a first support roller on which a part of the said ribbon is wound, the other end being fast with a second support roller, the first support roller being mechanically coupled to a first electric driving motor through a reversible reduction gear, the second support roller being likewise coupled to a second electric driving motor through another reversible reduction gear, the said motors being induction motors whose inductor winding may be energised either with direct current or with alternating current, the said system comprising a clutch disposed between each reduction gear and the associated support roller to connect each roller to the associated motor, the said clutches being adapted to be energised either with a relatively weak direct current to enable them to slip, or with a stronger direct current for maintaining them in the firmly engaged condition, an irreversible speed-changing device disposed between the clutch of the first roller and the reduction gear associated therewith, and switching means so designed that when the clutch of the first roller is in the firmly engaged condition and the first motor is energised with alternating current for winding the ribbon on to the first roller, a tension of the ribbon is obtained either by energising only the clutch of the second roller with a direct current of high strength, or by energising this clutch in such manner that it slips and simultaneously energising the second motor with direct current, while when the clutch of the second roller is in the firmly engaged condition and the second motor is energised with alternating current to wind the ribbon on to the second roller, the tension of the ribbon is obtained by energising the clutch of the first roller in such manner that it slips, it not being possible for the first motor to be driven by the ribbon owing to the irreversibility of the speed-changing device.

Further features of the invention and the manner in which the invention is put into practice will become apparent from the following description, which is given by way of example, with reference to the accompanying drawings, in which:

FIGURE 1 is a diagrammatic view in perspective indicating the relative positions of the ribbon, the type drum and various parts in the machine;

FIGURE 2 is a diagrammatic view in section along the line 2-2 of FIGURE 3 of the drum-ribbon mechanism;

FIGURE 3 is a fragmentary section along the line 33 of FIGURE 2 through various members of the left-hand part of the drum-ribbon mechanism;

FIGURE 4 is a first part of the diagram of the electric circuits for monitoring and controlling the movements of the ribbon;

FIGURE 5 is a second part of the diagram of the electric circuits for monitoring and controlling the movements of the ribbon, and

FIGURE 6 is a third part of the diagram of the electric circuits for monitoring and controlling the movements of the ribbon.

The machine which will now be described by way of example is a high-speed printing machine comprising a type drum, similar to that already described and illustrated in patent application Ser. No. 436,108, filed in the United States by Mr. Michel Andre Robert Bernard on Mar. 1, 1965, now Patent No. 3,291,043 issued Dec. 13, 1966. For the constructional details of the printing machine, reference may be made to said United States patent application. However, it is desirable to recall here with reference to FIGURES 1 and 2 that the printing machine comprises a type drum 1il2 which rotates at constant speed and past which there travels a paper web 139 and a printing ribbon 101. A striker mechanism assembly 114 is disposed opposite the drum in such manner as to apply the paper and the ribbon to the drum for a very brief time and thus to effect the printing of the paper. The printing takes place at the level of a line 107 called the printing line.

The printing machine just described by Way of example may be employed both for printing standard characters and for printing characters intended to be visually identified or to be scanned by an automatic reading device. In the latter case, the machine is designed to oper ate with a total-transfer dry ribbon which must be driven at relatively high speed. It will be recalled that the totaltransfer dry ribbon must be moved very rapidly at the end of the printing of a line through a distance sufiicient to prevent the inked portion which is then positioned opposite the striker hammers, from interfering, before the printing of the succeeding line, with that portion of the ribbon which has previously been used. It follows that such a ribbon is subjected to very considerable accelerations and decelerations which, in the described example, are obtained by means of electromagnetic clutches. Moreover, its use requires that its feed should be monitored by monitoring means which will shortly be described. In addition, it is essential that the said ribbon be maintained taut in order not to smudge the paper. Means which will, hereinafter be described are provided to ensure an appropriate tension of the ribbon.

FIGURE 1 shows that, in all cases of use, the ribbon 101, which optionally may be a total-transfer dry ribbon, is secured by its two ends to a first support roller 103 and to a second support roller 104, respectively, by means of flexible bands 105 and 105, each of which is provided With a bar 108 and a bar 109 respectively. These bars serve to close under conditions which will hereinafter be specified electric contact-s C11 and CIS intended to control the reversal of the ribbon. At a point close to the upper support roller 103, the ribbon 101 passes over the roller 112 by which, as will hereinafter be seen, the effective advance of the ribbon can be monitored. The said roller, which is adapted to turn freely about its axis, is rotated by the friction of the ribbon when the latter is in movement. It is to be noted that the total-transfer dry ribbon generally consists of a web of paper or flexible plastics, such as the plastics known commercially under the name Mylar for example, and on the surface of which there has been deposited an appropriate magnetic or non-magnetic ink which is completely transferable during the printing. Consequently, this ribbon, which may be relatively fragile, has to provide only a moderate effort for driving the roller 112 by which its feed is monitored. The described construction utilises a photo-electric device for monitoring the feed, which satisfies this requirement, but it is to be understood that this device, which will now be described, may be replaced by any other equivalent feed-monitoring device which only requires a relatively small effort from the ribbon in order to be set in operation. In the described example, the roller 112 is covered by a layer of rubber intended to increase the adhesion necessary to enable it to be driven by the ribbon. As will be seen in FIGURE 1, the said roller 112 is provided, at its end, with a slotted disc 213 which intercepts or allows to pass a beam of light emitted by a light source 211 and sent to a photo-electric cell'214. The cell 214 and the source 211 are enclosed in a casing 210, which is illustrated in FIGURES 2 and 3. Each time a slot in the disc 213 allows the passage of the beam of light directed towards the cell 214, the latter sends an electric signal to an amplifying device AMP. The ribbon 101 is guided (FIGURES 1 and 2) past the printing line 107 by means of two rollers 117 and 118 which maintain the said ribbon in immediate proximity to the drum 102 without, however, touching it. A guide roller 119 disposed above the drum guides the ribbon close to the lower support roller 1%.

The upper support roller 103 is normally engaged between two chucks namely an upper driving chuck 150 illustrated in FIGURE 3 and disposed at one of the two ends of the roller 103, and a similar upper support chuck (not shown) disposed at the other end. The upper support chuck turns freely about its axis and is brought into engagement with the roller 103 in known manner. Likewise, the lower support roller 104 is engaged between two chucks, namely a lower driving chuck 151 shown in FIG- URE 3 and a lower support chuck (not shown). However, it should be noted that the length of the upper support roller 103 differs in accordance with whether the ribbon employed is a total-transfer dry ribbon or not. In the case of the use of a total-transfer dry ribbon, the

upper support roller is shortened to enable a bladed nonreturn device 240 to be mounted on the driving chuck in accordance with the diagram of FIGURE 3 to prevent the upper support roller from turning in reverse under the action of the tension of the ribbon. FIGURES 2 and 3 show that the said non-return device consists of a sleeve 241 which may be fitted around the upper driving chuck 150 and which has on its periphery a series of flexible blades 242 which rub against the inner rim of a shoe 243, which is in turn secured to a support member 154. In addition, the sleeve 241 serves as a support for the upper support roller. The flexible blades 242 are so disposed as to oppose the rotation of the upper support roller in the direction opposite to that in which the ribbon is wound on to the said roller. Of course, the non-return device just described may be replaced by any equivalent non-return device. If the ribbon employed is not a total-transfer dry ribbon, this non-return device is omitted in order to enable the ribbon to perform successive travels in alternate directions.

The driving chucks 150 and 151 are each mounted, as indicated in FIGURE 3, with the interposition of ball bearings in support members 154 and 155' let into the frame of the machine. The chucks are each provided with a conical portion which may be engaged either in one end of a ribbon support roller or in the sleeve of a non-return device. This conical portion is in addition formed with striations 149 designed to increase the necessary adhesion between the said driving chucks and the ribbon support rollers, or in the case of the use of a totaltransrer dry ribbon, between the upper driving chuck and the sleeve of a non-return device. The upper driving chuck 150 is coupled to a first motor MRS through a reduction gear RS, a speed-changing device CV and a clutch WS. The lower driving chuck 151 is coupled to a second motor MRI through a reduction gear RI and a clutch WI. In the described example, the clutches WS and WI are known electromagnetic clutches of the type in which a continuously rotating driving shaft is provided with a cylindrical magnetic circuit, in the body of which there is disposed an excitation coil, which, when energised, produces the attraction of a friction disc which is fast in rotation with a shaft to be driven. The invention is not limited to the adoption of this type of clutch. The strength of the current flowing through the excitation coil is so adjusted that the magnetic attracting force by which the disc is maintained against the magnetic circuit is exerted either with a low value which is just suflicient to maintain the disc weakly applied against the magnetic circuit and thus to cause the clutch to slip, or with an appreciably higher value to keep the disc firmly applied to the magnetic circuit. Of course, in the absence of current, the disc is maintained at a distance from the magnetic circuit by known means. The clutches WS and W1 are diagrammatically illustrated at WS and WI in the diagram of FIGURE 5. The motors MRS and MRI are single-phase induction motors of known type, the particular operating conditions of which will shortly be described, and which are diagrammatically illustrated at MRS and MRI in the diagram of FIGURE 6. The speedchanging device CV is a pinion and spur-wheel device of known type comprising a driving shaft 221, a driven shaft 222 and an intermediate-pinion support 223 adapted to pivot about the driving shaft 221 and to be driven and then held fast in two different positions by means of an operating button 220, so as to provide different reduction ratios. A lever 22 i fast with the pinion support 223 is provided to close one of two switching elements, here consisting of two electric contacts C3 and C30, when the said support is brought into each of its two positions. In one of these two positions, the shaft 222 is driven at low speed, of the order of three revolutions per minute, while the contact C3, or first switching element, is closed by the lever 224. In the other position, the shaft 222 is driven at a relatively high speed, of the order of thirty revolutions per minute, while the contact C30, or

second switching element, is closed by the lever 224. For reasons which have already been explained in the foregoing, this relatively high speed is utilised in the case of the drive of a total-transfer dry ribbon. The reduction gears RS and RI are reversible, while the speed-changing device which drives the shaft 222 either at low speed or at high speed has a reduction ratio which does not permit it to be reversible. Consequently, if the coils of the clutches WS and WI are energised and if the upper support roller is driven by the motor MRS, the motor MRI is driven by the lower support roller under the effect of the traction exerted on the ribbon by the motor MRS. n the other hand, if the disc of the clutch WI is firmly held in engagement, and if the lower support roller is driven 'by the motor MRI, the motor MRS cannot, owing to the irreversibility of the speed-changing device CV, be driven by the upper support roller which turns under the effect of the traction of the ribbon. Under these conditions, in order to avoid danger of tearing of the ribbon, the disc of the clutch WS is not firmly engaged. However, in the latter case the coil of the clutch WS may be weakly energised so that this clutch, which is driven by the upper support roller, slips and then brakes the movement of the upper support roller, whereby it is possible to ensure an appropriate tension of the ribbon during its travel.

For a rational utilisation of the ribbon, whether it be of the total-transfer dry type or not, it is desirable that it should be automatically fed forwards as a function of the printing operations performed by the machine. This automatic feed is efifected by switching means which are controlled partly by the contacts C3 and C34) and which will now he described with reference to FIGURES 4, 5 and 6. The electric circuit diagram of FIGURES 4, 5 and 6 is a basic diagram of the circuits monitoring the movements of the ribbon, and comprises manually controlled contacts comprising relays, which are designed to be used under the conditions which will be described. FIGURES 4, 5 and 6 relate to the same circuit diagram, in which the +48-volts, -48-volts direct-current supply is common to the diagrams of these figures. The relay contacts are denoted by the same reference as the winding by which they are controlled, preceded by the letter C. A contact which is normally closed when the coil of the relay controlling it is not energised is represented in these diagrams by a black triangle.

The motors MRS and MRI illustrated in FIGURE 6 may be supplied either with single-phase alternating current or with direct current, as will hereinafter be described, under the control of first reversing devices consisting, in the example described, of three contacts CH05, CN05 and C105. The clutches WS and WI, which are illustrated in FIGURE 5, may be energised, as will hereinafter be seen, either with strong direct current or with reduced direct current, by the control of a second reversing device CK02, of a third reversing device C007 and of a first interrupting member CPOZ. Finally, a second interrupting member CNO6, shown in FIGURE 6, completes the supply control circuit of the motors MRS and MRI and enables them to be supplied with direct current from +48-volts. The selective supply of the motors MRS and MRI with alternating current or direct current is controlled :by means of two selecting relays CT6 and CT7.

When the circuits controlling the feed of the ribbon are in the inoperative state, three relays H04, H05 and H06 (FIGURE 6) are not energised. A capacitor C601 of 600 microfarads is maintained charged at 48 volts through a normally closed contact CI-I06 and a resistor R223. A relay H07 which is energised at the same time maintains its contact CH07 closed. Owing to the fact that the relay H05 is not energised, its contact CHOS is maintained in the off position. As long as the manual contact C3 shown in FIGURE 4 is not closed by the lever 224 of the speed-changing device CV, three relays M05, N05 and 005 remain unenergised. In this case, the conbon, the lever 224 of the speed-changing device CV is tact CNO (FIGURE 6) of the relay N05 is maintained in the oif position and thus produces the energisation of the relay CT6. The relay CT6 which is energised changes over its contacts CT61 and CT62, which then supply the indctor MRS of the upper motor with singlephase 22.0-volts alternating current supplied by two terminals 220 MN. The upper motor then rotates, but the inductor MRI of the lower motor is not supplied with alternating current owing to the fact that the relay CT7 (unenergised) maintains its contacts CT71 and CT72 .in the off position. On the other hand, the inductor MRI of the lower motor cannot be supplied from +48- volts through a resistor R18 of low value owing to the fact that the contact CN05 is in the off position and that a relay N06 (FIGURE 4), which is not energised as .long as the contact C30 is maintained open, maintains its contact CNOS open. FIGURE 5 shows that, under these conditions, a relay M06 (FIGURE 4) which is not energised owing to the fact that the contact C30 is open, maintains its contact CM06 open. Consequently, three the ribbon support rollers are unaffected by the movements of the motors.

Manual control 0 the ribbon feed-It may be essential to feed the ribbon either in order to obtain uniform quality of the printing from the outset or in order to .tension the ribbon after it has been placed in position.

As will hereinafter be seen, the feed is effected by operation of a push button TR shown in FIGURE 4. In the unoperated position, this button TR energises a relay N07 through its contact CTR.

If the ribbon employed is not a total-transfer dry ribbrought to the position corresponding to the drive of the shaft 22 at low speed and thus closes the contact C3 (FIGURE 4). The relays MOS, N05 and 005 ,are then energised, whereby the contacts CMOS and C005 are closed, and the contact CN05 is reversed (FIGURES 4, 5 and 6). The closing of the contact C005 results in energisation of the relays E01 and E02. The cont-acts CEOI and CE02 then close, so that direct current can be supplied from +48-volts on the one hand to the clutch WI through the closed contact CE02 and on the other hand to the clutch WS through the closed contacts CE02 and CEOI and the contact C007 in the off position. On the other hand, the relay CT6 can no longer be energised owing to reversal of the contact CN05. The cont-acts CT61 and CT62 then fall back and the inductors of the motors MRS and MRI then receive direct current through the contact CN05, the contact CHOS maintained in the off position and the resistor R18. If, at this instant, the push button TR (FIGURE 4) is depressed for a prolonged period in order to reverse the contact CTR, the relay N07 is de-energised and then changes over its contact CNO7 (FIGURE 5) in order to energise two relays P02 and K03. The contact CF02 closes and the direct current which then flows from +48-volts through the contacts CE02, CEOl, C007 and CF02 energises a relay G02. The action of the said relay G02 momentarily has no effect on the feed of the ribbon. The energised relay K03 opens its contact CKO3, thus bringing two relays B04 and B05 into the unoperated condition should they have been energised by the closing of the contact CBO3 of a relay B03. Moreover, reversal of the contact CTR brings three relays J04, I05 and 006 (FIGURE 4) into the unoperated condition should they have been energised by closing of the contact C103 of the relay J03. Finally, reversal of the contact CTR results in energisation of the relay H03 (FIGURE 4), since the contact CMOS has already been closed by closing of the contact C3. The relay H03 then reverses its contact CH03 (FIGURE 6). The relays H04 and. H are temporarily energised through the reversed contact CH03, and are maintained energised by closing of the contact CHO4, the contact CI-I07 having already been closed by the energised relay H07. The energised relay H05 reverses its contact CHOS. Since the relay N05 has already been energised by closing of the contact C3, a direct current passes through the contacts CNOS, CHOS, C105 and energises the relay CT6, which changes over its contacts CT61 and CT62, which then supply 220-volts current to the inductor of the motor MRS. In addition, reversal of the contact CHOS interrupts the direct-current supply to the inductor of the motor MRI. Under these conditions, the motor MRS rotates and drives the shaft 222 at a speed of three revolutions per minute, as also the upper support roller 103, since the clutch WS is firmly engaged by the direct current. As long as the push button TR is maintained in the depressed position, the ribbon is driven by the motor MRS and in turn drives the (unsupplied) motor MRI through the lower support roller 164 and the clutch WI, which is firmly engaged by the direct current. The drive of the motor MRI and the clutch WI constitutes a resistant torque sufiicient in practice to ensure an appropriate tension of the ribbon.

When the push button TR for the manual control of the movement of the ribbon is released, the contact CTR returns to its ofi position and the relay H03 is no longer energised. The relay N07 is again energized. The contact CH03 (FIGURES 4 and 6) falls back and the relay H06, which is then energised through the contacts 01-107, 01-104 and CH03, opens its contact CH06. From this instant, H07 is energised only by the discharge of the capacitor C661, through the resistor R223. The useful discharge of the capacitor lasts about two seconds. Thereafter, owing to the fact that the relay H07 is no longer energised, the contact CI-I07 opens and the relays H04, H05 and H06 are brought into the unoperated state. The contact CH06 falls back and the capacitor C601 is again charged through the resistor R223. The contact 'CHOS also falls back and, since the relay GT6 is no longer energised, the contacts CT61 and CT62 {all back into the ofi position. The inductors of the motors MRS and MRI are then supplied with direct current through the contacts CNOS, CI-IOS and the resistor R18. This arrangement has the object of strongly braking the motors in order to maintain the ribbon in the tensioned state and thus to avoid smudging of the printing paper. In addition, energisation of the relay N07 results in the change-over of the contact CNO7 (FIGURE 5) and deenergises the relays P02 and K03. The contact CPOZ opens, whereby energisation of the relay 602 is interrupted, while the contact CKO3 returns to its off position.

On the other hand, if the ribbon employed is a totaltransfer dry ribbon, the feed of the ribbon takes place in the following manner. The lever 224 of the speed-changing device CV is brought to the position corresponding to the drive of the shaft 222 at high speed and thus closes the contact C30 (FIGURE 4). The relays M06 and N06 are then energised, whereby the contacts CM06 (FIGURE 5) and CNO6 (FIGURE 6) are closed. Closing of the contact CM06 results in energisation of the relays M07, M08 and M0? which, is turn, close their contacts CMO7, CMOS and CM09. Since the contacts CMO7 and CMOS are closed, the clutch WI receives direct current from +48-volts through the contacts CMO7, CM08 .and CK02 and through a resistor R7. The function of the resistor R7 is to limit the direct current then supplied to the clutch WI to an appropriate value for obtaining slipping of this clutch. 0n the other hand, direct current can be supplied to the relay G02 through the contacts CMO7 and C008. The contact C002 closes, but this for the moment has no effect on the feed of the ribbon. The contact CM09 being closed and the relay N07 being energised through the contact CTR which is then in the off position, ,a direct current energises, through the contacts CNO7, CM09 and CF03 (FIGURE 5), the relay K01, which closes its contact CKOI. In addition, since the contact C3 (FIGURE 4) is open, the relays M05, N05 and 005 are not energised, and in particular the contact CNOS (FIGURE 6), which is then in the off position, energises the relay CT6. The inductor of the motor MRS is then supplied with alternating current at 220 volts, since the contacts CT61 and (BT62 of the relay-CTe have changed over. Finally, since the relay N05 (FIGURE 4) is energised owing to the fact that the contact C3tl is closed, the contact CN06 (FIGURES) is closed and thus enables direct current to be supplied to the inductor of the motor MRI through the resistor R18 and the contacts CT71 and CT'72 of the unenergised relay CT7. It, ,at this instant, the push button TR (FIGURE 4) is depressed for a prolonged period in order to reverse the contact CTR, the relay N07 is deenergised and then changes over its contact CNO7 (FIG- URE 5), The relays P02 and K03 are consequently energised, while the relay K01 is de-energised. The contacts OKOI and CK03 open, while the contact CF02 closes. It will be noted that on depression of the push button TR further energisation of the relay H03 (FIG- URE 4) is not possible, since the contact C3 is open and, consequently, the contact CMOS of the relay M05 is open. It will also be noted that depression of the push button TR has the effect of bringing the relays B04 and B05 into the unoperated state through the energised relay K03 and its contact CK03, as .also the relays J04, J05 and 006 should they have been energised. Referring again to FIGURE 5, it will be observed that closing of the contact CF02 enables the clutch WS to be supplied with direct current from +48-volts through the contacts =CM05, C008 and CF02. Under these conditions, the motor MRS drives the upper support roller 103 through the clutch WS, which is firmly held in engagement, at a speed of thirty revolutions per minute. The ribbon then drives in its movement the lower support roller 104. The continuous magnetic field produced by the current which energises the inductor of the motor MRI brakes the rotor of this motor, which is driven by the movement of the ribbon, through the clutch II, which slips. The slipping of the clutch WI prevents sudden tensioning of the ribbon, which would result in tearing of the latter at starting.

When the push button TR is released, the contact CTR returns to its off position and the relay N07 is energised again. The change-over of the contact CNO7 (FIGURE 5) enables the relay K01 to be energised through the contacts CM09 and CF03, While the relays P02 and K03 are de-energised. The contact CPOZ opens and the clutch WS ceases to be supplied with direct current. The motor MRS continues to rotate, but it no longer drives the ribbon, since the clutch WS is no longer energised. The ribbon ceases to advance, since it is braked by the motor MRI, which remains connected to the lower support roller since the clutch WI continues to be energised. 0n the other hand, the non-return device 240 which is used in the case of the total-transfer dry ribbon, prevents the upper support roller from turning in reverse, which enables the tension of the ribbon to be maintained.

Automatic ribbon feed under normal conditions 0] use of the machine.During normal operation of the machine, the ribbon -feed is maintained by control pulses which, in the described example, emanate from the paper feed control circuits and are transmitted to the ribbon feed control circuits through a line CSP (FIGURES 4 and 5) at the end of the printing of each line of characters on the paper, i.e. at intervals of time of 200 milliseconds in the case of the machine being described.

In cases Where the ribbon employed is not a total-transfer dry ribbon, the contact C3 is closed by the lever 224 of the speed-changing device CV, whereby the relays M05, N05 and 005 are energised. As has already been described in the foregoing, closing of the contact C005 of the energised relay 005 results in energisation of the relays E01 and E02 which, in turn, close their contacts CEOl and CE02, Consequently, the clutches WS and WI are supplied with direct current, as has already been explained. Energisation of the relay N05 has the effect of reversing the contact CNOS, which then ceases to energise the relay T6. Finally, the contact CM is closed owing to energisation of the relay M05. The relay N07 is energised because the contact CTR is in the off position, and consequently the relays P02 and K03 (FIG- URE 5) cannot be energised, since the contact CN07 is in the on position. Consequently, the contact CF02 is open, the relay G02 is not energised and the contact CK02 is open. The feed pulses are systematically applied to a relay K08 (FIGURE 4) which closes a contact CK08, whereby a relay J08 is energised and then closes a contact CJO8. The contact CMOS already being closed, it follows that the relay H03 is then energised and reverses its contact CH03. Since the control pulses transmitted through the line CSP may be of short duration, a capacitor C15 connected in parallel with the relay J08 through a resistor R221 prolongs by about 60 milliseconds the closing time of the contact C108. During this time, the relay H06, which is normally energised through the off contact CH03, can no longer be energised and the capacitor C601 can be recharged through the off contact CH06. Since the relay N05 is energised and the contact CH03 has been changed over, the cycle which is then initiated is similar to that produced by depression of the push button TR in the case of the use of a ribbon other than a total-transfer dry ribbon. This cycle has already been described and for this reason it will merely be recalled that the motor MRS is supplied with alternating current at 220 volts while the motor MRI is not supplied. It will also be recalled that the clutches WS and WI are firmly held in engagement and that the period of the useful discharge of the capacitor C601 through the resistor R223 is about two seconds. Thus, as long as control pulses are transmitted to the relay K08, the drive of the ribbon is continuous, since these pulses are transmitted at time intervals of 200 milliseconds.

If, on the other hand, the ribbon employed is a totaltransfer dry ribbon, the lever 224 of the speed-changing device CV is so positioned that the contact C30 is closed. Under these conditions, the relays M06 and N06 are energised, while the relays M05, N05 and 005 are not energised. As has already been explained, the contact CNOS is then in the off position and the contact CN06 is closed, which results in a supply of 220-volts alternating current to the motor MRS, while the motor MRI is supplied with direct current. It will also be recalled that closing of the contact CM06 results in closing of the contacts CM07, CMOS and CM09. A direct current can then be supplied through the contacts CM07, CMO8, CK02 and the resistor R7 to the clutch WI, which can then slip since it is only weakly engaged. The relay G02, which is energised through the contacts CMOS and C008, closes its contact CBO2. The relays P02 and K03 are not energised, while the relay K01, which is energised through the contacts CN07, OM09 and CF03 closes its contact CKO1. As before, the feed pulses are applied to the relay K08, but, since the contact CG02 is now closed, these pulses are also applied to a synchronising circuit, which will now be described. The said pulses arrive at a relay F04 (FIGURE 5), which closes its contact CF04, as also at a delay element D55. It should be noted that the contact CMOS is open and that consequently the pulses applied to the relay K08 can no longer energise the relay H03. During the brief instant when the contact CF04 is closed, a direct current energises the relay F03 and charges a 10 capacitor C701 through the contacts CN07, CMO 9, CF04 and a diode D1. The energised relay F03 changes over its contact CF03, whereby the relays P02 and K03 are energised and the relay K01 de-energised. The capacitor C701, which is connected in parallel with the relay F03 through a resistor R11, extends by 35 milliseconds the time during which the contact CF03 is changed over. During this time, the de-energised relay K01 opens its contact CK01, the energised relay K03 opens its contact CKO3, and the energised relay P02 closes its contact CP02, whereby the clutch WS is energised. Opening of the contact CK01 prevents stop pulses which come from the feed monitoring device previously described with reference to FIGURE 1 from the transmitter to a relay B01 through the amplifying device AMP. The motor MRS, which is supplied with current at 220 volts, then drives the ribbon, which remains tensioned owing to the slight braking action exerted by the motor MRI, through the clutch WI. At the end of 35 milliseconds, the de-energised relay F03 changes over its contact CF03 into the off position, whereby the relay K01 is again energised and the relays P02 and K03 de-energised. The contacts CK01 and CKO3 are then closed, while the contact CPOZ is opened and de-energises the clutch WS. The motor MRS, which is still supplied with current at 220 volts, is then disengaged from the upper support roller and ceases to drive the ribbon. The motor MRI, which is supplied with direct current, continues to brake the ribbon slightly through the clutch WI, which slips. The ribbon is thus maintained in the tensioned condition. If at this instant a stop pulse coming from the feed control device is transmitted to the relay B01 through the amplifying device AMP and the closed contact CK01, a contact CB01 closes, whereby two relays K02 and B03 are energised. The pulse which energises the relay B01 for a very brief time is also transmitted through a diode D2 to a capacitor C702. The capacitor C702, which is connected in parallel with the relay B01 through a resistor R12, extends by 15 milliseconds the time during which the contact CB01 is closed. During this time, the energised relay B03 closes its contact CB03. The contacts CK03 and CB02 being closed, the relays B04 and B05 are energised. The relay B04 then closes its contact CBO4 and thus establishes a holding circuit for the relays B04 and B05. The energised relay B05 reverses its contact CBOS. During the time when the contact CB01 is closed, the energised relay K02 reverses its contact CK02. The clutch WI, which then receives an intense direct current, is firmly engaged. The motor MRI, which is thus firmly engaged with the lower support roller, strongly brakes the ribbon and rapidly stops it. The non-return device causes an appropriate tension of the ribbon while stationary. The stopping is substantially obtained before the relay B01, which is de-energised at the end of 15 milliseconds, opens its contact CB01. The relays K02 and B03 are then de-energised and the contact CK02 returns to its off position. It will be appreciated from the explanations just given that, from the instant when a feed pulse is applied to the relay F04, the ribbon is driven for 35 milliseconds by the motor MRS, and that it thereafter ceases to be driven. If, at the end of these 35 milliseconds, a stop pulse is applied to applied to the relay B01, the ribbon is rapidly stopped. It is to be noted that this time of 35 milliseconds corresponds to a linear displacement of the ribon of the order of 3.15 millimetres. Since the height of the characters printed on the paper does not exceed 2.7 millimetres, this displacement is sumcient to prevent the inked portion of the ribbon which is then positioned opposite the striker hammers from interfering with that portion of the ribbon which has been used in the preceding striking action. Consequently, during these 35 milliseconds, the contact CK01 remains open so as to prevent a stop pulse from energising the relay B01 and thus initiating the premature stoppage of the movement of the ribbon. However, the ribbon must be stopped at the instant of the printing. The continuous drive of a total-transfer dry ribbon moved at a linear speed of the order of 9 centimetres per second would result mainly in an excesive consumption of the ribbon. Consequently, having regard to the characteristics of the machine, the ribbon must be moved only for an interval of time which does not exceed 70 milliseconds. Owing to the fact that the time necessary for stopping the ribbon is of the order of to milliseconds, it is essential that the stop pulse which emanates from the feed monitoring device he applied to the relay B01 at the latest 50 milliseconds after the application of a feed pulse to the relay F04. This necessity is met by an appropriate positioning of the slots in the disc 213 of the feed monitoring device. Thus, during normal operation, as long as feed pulses are transmitted to the relay F04 at intervals of time of 200 milliseconds, the ribbon is periodically moved step-bystep.

Monitoring of the ribbon feed.The monitoring of the efiective feed of the ribbon is carried out with the aid of the feed monitoring device, which sends ribbon stop pulses to the relay B01 through the amplifying device AMP and the contact CK01. The monitoring is efrected only when the ribbon employed is a total-transfer dry ribbon. In other cases, the contact CKOl remains open, since the open contact C does not enable, in particular, the relay M09 to be energised, and consequently the relay K01 is not energised. The appropriately tensioned total-transfer dry ribbon drives by friction during its movement the roller 112, on the end of which is mounted the slotted disc 213. When a feed pulse is applied to the relay F04, the ribbon is driven for milliseconds, as has been seen in the foregoing, thereafter ceases to be driven and is finally stopped by a stop pulse which is applied to the relay B01. This stop pulse, which emanates from the feed monitoring device, can be applied to the relay B01 only after the instant when the ribbon ceases to be driven, but during normal operation it must not be sent after the 15 milliseconds which succeed this instant, in order that the ribbon may be actually stationary at the instant when the striking is resumed. The feed control pulse which energises the relay P04 is also applied to the delay element D55, at the output of which it appears with a delay of 55 milliseconds. A contact CB05 controlled by the relay B05 then transmits it either to a feed incident signalling device D81 or to a relay B02 and to a delay element D15. If a stop pulse reaches the relay B01 at the latest 50 milliseconds after the application of a feed control puls to the relay F04, the contact CBOl closes and thus energises the relays K02 and B03. On closing, the contact CB03 establishes the holding of the relays B04 and B05. Consequently the contact CB05 is changed over before the feed control pulse, delayed by 55 milliseconds, is set up at the output of the element D55. This delayed pulse is then transmitted on the one hand to the delay element D15 and on the other hand to the relay B02, which is energised and opens its contact CB02. The relays B04 and R05 are no longer energised and the contact CBO4 breaks the holding circuit of these relays, while the contact CBOS returns to the o position. During this time, the pulse transmitted to the element D15 is delayed by 15 milliseconds, which is the maximum time after which the ribbon is stopped, in order to set up an end-of-feed signal FAR for the ribbon, which signal is in turn utilised to initiate the resumption of the striking. If, on the other hand, a stop pulse reaches the relay B01 after the 50 milliseconds following the application of a feed control pulse to the relay F04, for example because the ribbon is insufiiciently tensioned and therefore does not sufficiently drive the roller 112, or if no stop pulse reaches the relay B01, either because the feed monitoring device is defective or because the ribbon is torn or broken, the contact CB05 cannot be reversed before the feed control pulse, delayed by 55 milliseconds, is set up at the output of the element D55. This delayed pulse is then transmitted to the feed incident signallingdevice DSI. Resumption of the striking cannot be initiated and consequently the feed control pulses, which are normally transmitted at the end of the printing of each line, cease to be sent.

Reversal of the movement of the ribb0n.As has already been explained, any ribbon which is not a totaltransfer dry ribbon can perform a series of travels in alternate directions. Such a ribbon is then provided, near to its ends, with bars 10% and 109, shown in FIGURE 1, which are so arranged as to close, respectively, an electric contact CIS which detects the end of the ribbon on the upper roller and an electric contact CII which detects the end of the ribbon on the lower roller. If, for example, the contact C11 is closed as a result of the end of the ribbon on the lower roller, a relay J03, mounted as indicated in FIGURE 4, is energised and closes its contact C103. The contacts CTR and C102 being in the off position, the relays J04, J05 and 006 are then energised. The relay J04 establishes at +48-volts, through its contact C104, a holding circuit for itself and for the relays J05 and 006. It is worthwhile recalling here that the relay N05 (FIGURE 4) is energised as a result of the closing of the contact C3 and that the relay H05 (FIGURE 6) is continuously energised, provided that control pulses are transmitted to the relay K08. FIGURE 4 then shows that, owing to the energisation of the relay J05, the contact C105 is reversed, and that a direct current consequently energises the relay CT7 through the contacts CNOS, CI-I05 and C105. The relay CT6 ceases to be energised and returns its contacts CT61 and CT62 into the OE position, whereby the supply of alternating current to the motor MRS is interrupted. The energised relay CT7 brings its contacts CT71 and CT'72 into the on position for supplying alternating current to the motor MRI. It will be noted that the inductor of the motor MRS cannot be supplied with direct current because the relay H05 is energised and the contact CNO6 is open. Moreover, FIG- URE 5 shows that, as a result of the energisation of the relay 006, the contact C006 closes and permits the energisation of two relays 008 and 007. The contact C008 is changed over, and produces no action because the contacts CM07, .CMOS and CF02 are open. The energised relay 007 changes over its contact C007. The clutch WS then receives direct current from +48-volt-s'through the contacts CE02, CE01, C007 and a resistor R6. The function of the resistor R6 is to limit the direct current with which the clutch WS is supplied to an appropriate value for obtaining slipping of this clutch. 0n the other hand, the clutch W1 is firmly engaged by the direct current coming from +48-volts through the contact CEOZ.

Consequently, the ribbon is driven by the motor MRI ribbon to be driven, and ensures sufiicient braking to maintain the ribbon in the tensioned condition, since the motor MRS remains at standstill, as also does the irreversible speed-changing device. When the contact 018 consequently detects the end of the ribbon on the upper roller, a relay J02 shown in FIGURE 4 is energised and opens its contact C102. The relays J04, J05 and 006 are no longer energised, so that, on the one hand, the contact C105 changes over into the off position, .and on the other hand the contacts C104 and C006 are opened. The relay GT6 is again energised, thus enabling the motor MRS to be supplied with alternating current, while the motor MRI is not supplied. In addition, the relays 008 and .007, which are de-energised owing to the opening of the contact C006, change over their contacts C008 and C007 into the off position. The clutches WS and WI are again firmly engaged and the ribbon is then rewound on to the upper roller.

If, on the other hand, the ribbon which is employed is a total-transfer dry ribbon, it must not undergo any reversal of movement. As already explained, the said ribbon is moved step-by-step and thus wound on to the upper roller, and it is provided with a bar 109 which, at

:the end of the ribbon, then closes the electric contact CH. By a cycle similar to that already described, the relay J03 is energised and closes its contact C103, whereby the three relays J05, I04 and 006 are energised. The maintenance of the energisation of these three relays is effected by the relay J04. The contact C006 of the energised relay 006 closes and thus energises the relays 008 and 007. It will in addition be recalled that in the case of the use of a total-transfer dry ribbon the contacts CMO7 and CM08 are closed. The change-over of the contact C007 of the energised relay 007 does not result in any action, because the contacts CE01 and CE02. are open. The energisation of the relay 008 brings about the changeover of the contact C008. A direct current coming from +48-volts is then applied through the contacts CMO7 and C008 to an end-of-ribbon signalling device SFR which thus signals that the ribbon must be changed. At the same time, the clutch WS ceases to be energised owing to the change-over of the contact C008, and the relay G02 is de-energised. The motor MRS then ceases to drive the ribbon. The de-energised relay G02 opens its contact CG02 and thus prevents the feed pulses from be ng applied to the relay F04. Under these conditions, the restarting of the machine with a new ribbon can take place only after the push button TR has been depressed, whereby the holding of the relays J05, I04 and 006 will be terminated and consequently the contact C008 will change over to the off position.

Although the description and the accompanying drawings relate only to a preferred embodiment of the invention, it is to be understood that various modifications, additions and substitutions which do not depart from the scope of the said invention may be applied, depending upon the circumstances and applications, without the principle of the invention being changed. More particularly, the relay circuit diagram given by way of example may be completely or partly replaced by any other equivalent electric circuit utilising transistors, cryotrons, electron tubes or similar elements.

The characteristic points of the invention will be more clearly apparent from the following claims.

I claim:

1. In a system for moving an inked ribbon in a printing mechanism, in either of two opposite directions, or where necessary in only one direction, the combination comprising a first and a second driving roller, an inked ribbon whose two ends are each fixed to one of the said rollers, driving means for driving each roller separately in one direction and comprising for each roller an electric induction motor mechanically coupled to the said roller through an electromagnetic clutch, a speed-changing device disposed between the motor for driving the first roller and the clutch associated with the said roller for effecting the drive of the said roller at one of two different speeds, in dependence upon a previous manual positioning of the said device, an alternating-current source, a directcurrent source, and switching means for controlling the supply of current to the motors and to the clutches, the said switching means being controlled in dependence upon the manual positioning of the speed-changing device in such manner that, when the said device is brought into a first position, the clutch of the first roller is connected to the direct-current source for transmitting a maximum torque, the inductor of the motor of the first roller is connected to the alternating-current source for driving the said roller at high speed through the associated clutch, the clutch of the second roller is supplied with direct current of lower strength permitting slipping of the said clutch, and the inductor of the second roller is connected to the direct-current source for creating a magnetic braking field on the armature of the said motor and ensuring tensioning of the ribbon, while, when the said speed-changing device is brought to a second position, the clutch of the first roller is connected to the directcurrent source for transmitting a maximum torque, the

inductor of the motor of the first roller is connected to the alternating-current source for driving the said roller at reduced speed through the associated clutch, and the clutch of the second roller is connected to the directcurrent source for permitting maximum mechanical coupling between the second roller and the motor associated therewith in order to create on the second roller driven by the ribbon an opposed torque which ensures the tensioning of the said ribbon.

2. The combination according to claim 1, wherein the said switching means comprise a first control relay adapted to be energised or not energised by a direct-current source and adapted to actuate a make-and-break contact whose centre blade is connected to the said current source when the speed-changing device is brought into the second position, and two selecting relays each of which is adapted to actuate a make-and-break contact associated with the inductor winding of one of the said motors, in each of the make-and-break contacts of a selecting relay, the centre blade is connected to a terminal of the associated inductor winding, the make blade is connected to a terminal of the said alternating-current source and the break blade is connected to a common conductor, which conductor is connected to the break blade of the make-and-break contact of the first control relay, the make blade of the said contact being connected to the centre blade of a first reversing contact for supplying direct current to either one of the selecting relays, so that when the speed-changing device is brought into the second position the aforesaid make-and-break contacts are positioned, when the said first control relay is maintained in the energised condition, to permit the supply of alternating current to the inductor of one of the motors, while, when the first control relay ceases to be energised, the aforesaid make-andbreak contacts are positioned to pass a direct current through the inductors of the two motors so as to brake the armatures of the two motors.

3. The combination according to claim 2, wherein, in order to enable the ribbon to be wound on to the second roller, when the speed-changing device is brought into the second position, the switching means comprise a second and a third control relay which are adapted to be excited with direct current when the winding of the ribbon on to the first roller has been completed, the third control relay being adapted to actuate a second reversing contact whose centre blade is connected to a direct-current source when the speed-changing device is brought into the second position, the break blade being connected to a terminal of the clutch associated with the first roller, the make blade being connected to the said terminal through a relatively high resistance, the second control relay being adapted to actuate the first reversing contact, of which the break blade is connected to that of the two selecting relays which actuates the make-and-break contact associated with the motor driving the first roller, and of which the make blade is connected to the other selecting relay, so that when the first, second and third control relays are energised, this other selecting relay brings about the supply of alternating current to the inductor of the motor driving the second roller, while the second reversing contact is positioned to supply direct current through the aforesaid resistance to the clutch associated with the first roller, the strength of the said current being such as to cause the said clutch to slip and to ensure appropriate tensioning of the ribbon.

4. The combination according to claim 1, wherein the switching means comprise a group of control relays comprising a first and a second relay adapted to be energised with direct current when the speed-changing device is brought into the first position, and a synchronising circuit designed to effect the periodic energisation of the second of the said group of control relays, the first of the said group of control relays being adapted to actuate a first interrupting contact disposed between a direct-current source and a terminal of the inductor of the motor of 1. 5 the second roller, the second of the said group of control relays being adapted to actuate a second interrupting contact arranged to supply direct current to the clutch associated with the first roller, so that when the speed-changing device is brought into the first position the said second interrupting contact periodically closes under the control of the synchronising circuit in order periodically to supply direct current to the clutch associated with the first roller and to permit the periodic driving of the said roller by the corresponding driving motor.

5. The combination according to claim 4, wherein, for obtaining a step-by-step feed of the ribbon when the speed-changing device is brought into the first position, the switching means comprises a current control relay adapted to actuate a make-and-break contact whose centre blade is connected to a direct-current source, when the speed-changing device is brought into the first position, the make blade of the said contact being connected to a supply terminal of the clutch associated with the second roller, and the break blade of the said contact being connected to the said supply terminal through a relatively high resistance, a ribbon feed monitoring device being 5 ceases to be driven by the motor associated With the first roller the current control relay is energised in response to the despatch of a stop signal transmitted by the feed monitoring device and changes over its contact to enable the clutch associated with the second roller to be supplied 10 with strong direct current in order to enable a maximum mechanical coupling to be set up between the second roller and the associated driving motor and thus to ensure a strong braking.

References Cited 15 UNITED STATES PATENTS 3,291,043 12/1966 Bernard 10l336 X 3,334,722 8/1967 Bernard 1971 33 ROBERT E. PULFREY, Primary Examiner.

E. T. WRIGHT, Examiner. 

1. IN A SYSTEM FOR MOVING AN INKED RIBBON IN A PRINTING MECHANISM, IN EITHER OF TWO OPPOSITE DIRECTIONS, OR WHERE NECESSARY IN ONLY ONE DIRECTION, THE COMBINATION COMPRISING A FIRST AND A SECOND DRIVING ROLLER, AN INKED RIBBON WHOSE TWO ENDS ARE EACH FIXED TO ONE OF THE SAID ROLLERS, DRIVING MEANS FOR DRIVING EACH ROLLER SEPARATELY IN ONE DIRECTION AND COMPRISING FOR EACH ROLLER AN ELECTRIC INDUCTION MOTRO MECHANICALLY COUPLED TO THE SAID ROLLER THROUGH AN ELECTROMAGNETIC CLUTCH, A SPEED-CHANGING DEVICE DISPOSE BETWEEN THE MOTOR FOR DRIVING THE FIRST ROLLER AND THE CLUTCH ASSOCIATED WITH THE SAID ROLLER FOR EFFECTING THE DRIVE OF THE SAID ROLLER AT ONE OF TWO DIFFERENT SPEEDS, IN DEPENDENCE UPON A PREVIOUS MANUAL POSITIONING OF THE SAID DEVICE, AND ALTERNATING-CURRENT SOURCE, A DIRECTCURRENT SOURCE, AND SWITCHING MEANS FOR CONTROLLING THE SUPPLY OF CURRENT TO THE MOTORS AND TO THE CLUTHES, THE SAID SWITCHING MEANS BEING CONTROLLED IN DEPENDENCE UPON THE MANUAL POSITIONING OF THE SPEED-CHANGING DEVICE IN SUCH MANNER THAT, WHEN THE SAID DEVICE IS BROUGHT INTO A FIRST POSITION, THE CLUTCH OF THE FIRST ROLLER IN CONNECTED TO THE DIRECT-CURRENT SOURCE FOR TRANSMITTING A MAXIMUM TORQUE, THE INDUCTOR OF THE MOTOR OF THE FIRST ROLLER IS CONNECTED TO THE ALTERNATING-CURRENT SOURCE FOR DRIVING THE SAID ROLLER AT HIGH SPEED THROUGH THE ASSOCIATED CLUTCH, THE CLUTCH OF THE SECOND ROLLER IS SUPPLIED WITH DIRECT CURRENT OF LOWER STRENGTH PERMITTING SLIPPING OF THE SAID CLUTCH, AND THE INDUCTOR OF THE SECOND ROLLER IS CONNECTED TO THE DIRECT-CURRENT SOURCE FOR CREATING A MAGNECTIC BRAKING FIELD ON THE ARMATURE OF THE SAID MOTOR AND ENSURING TENSIONING OF THE RIBBON, WHILE, WHEN THE SAID SPEED-CHANGING DEVICE IS BROUGHT TO A SECOND POSITION, THE CLUTCH OF THE FIRST ROLLER IS CONNECTED TO THE DIRECTCURRENT SOURCE FOR TRANSMITTING A MAXIMUM TORQUE, THE INDUCTOR OF THE MOTOR OF THE FIRST ROLLER IS CONNECTED TO THE ALTERNATING-CURRENT SOURCE FOR DRIVING THE SAID ROLLER AT REDUCED SPEED THROUGH THE ASSOCIATED CLUTCH, AND THE CLUTCH OF THE SECOND ROLLER IS CONNECTED TO THE DIRECTCURRENT SOURCE FOR PERMITTING MAXIMUM MECHANICAL COUPLING BETWEEN THE SECOND ROLLER AND THE MOTOR ASSOCIATED THEREWITH IN ORDER TO CREATE ON THE SECOND ROLLER DRIVEN BY THE RIBBON AN OPPOSED TORQUE WHICH ENSURES THE TENSIONING OF THE SAID RIBBON. 